Units 1-8 Ap Bio Lecture Notes
Unit 1 đ˘
Unit 1
The Study of Life
Biology is the scientific study of life.
Properties of life include: Â Â - Order: Organisms are complex and organized. Â Â - Regulation: Homeostasis, such as body temperature regulation in mammals. Â Â - Growth and Development: Organisms grow and develop according to specific instructions coded for by their genes. Â Â - Energy Processing: Living organisms take in energy to perform work. For example, plants convert sunlight into chemical energy via photosynthesis. Â Â - Response to the Environment: Organisms respond to environmental stimuli. For instance, plants grow towards light. Â Â - Reproduction: Organisms reproduce their own kind, either sexually or asexually. Â Â - Evolution: Populations of organisms evolve over time.
The Scientific Method
The scientific method is a systematic approach to understanding the natural world and includes: Â Â 1. Observation: Gathering information in a systematic way. Â Â 2. Question: Asking a question based on observations. Â Â 3. Hypothesis: Formulating a testable explanation based on observations. Â Â 4. Experiment: Testing the hypothesis through experimentation. Â Â 5. Analysis: Analyzing data to draw conclusions about the hypothesis. Â Â 6. Conclusion: Determining whether to reject or fail to reject the hypothesis. If rejected, reformulate a new hypothesis.
Themes in Biology
Evolution: The core theme that unifies all of biology, describing the descent with modification from common ancestors over time.
Structure and Function: The relationship between structure and function in biological systems, exemplified in various forms of life.
Information Flow: The concept that information is passed from one generation to the next through DNA; gene expression governs the characteristics of organisms.
Energy and Matter: The flow of energy and cycling of nutrients are essential to the survival of organisms.
Interactions: Biological systems interact, and these interactions can result in complex behaviors and emergent properties.
Levels of Biological Organization
Atoms: The basic units of matter.
Molecules: Groups of atoms bonded together (e.g., DNA).
Cells: The basic unit of life, can be prokaryotic or eukaryotic.
Tissues: Groups of similar cells performing a specific function.
Organs: Structures composed of different tissues serving a specific function.
Organ Systems: Groups of organs that work together.
Organisms: Individual living entities.
Populations: Groups of organisms of the same species living in the same area.
Communities: Different populations living and interacting in a particular area.
Ecosystems: Communities interacting with their physical environment.
Biosphere: The global sum of all ecosystems.
Basic Chemistry for Biology
Atoms: Comprised of protons, neutrons, and electrons. The atomic structure influences the chemical properties of elements.
Ionic Bonds: Formed when one atom transfers electrons to another atom, resulting in charged ions.
Covalent Bonds: Formed when two atoms share one or more pairs of electrons, creating molecules.
Hydrogen Bonds: Weak attractions between molecules or within a single molecule (e.g., between water molecules).
Water: Essential for life, it has unique properties such as being a polar solvent, having a high heat capacity, and being less dense as a solid than a liquid.
The Cell Theory
The cell is the basic unit of life.
All living organisms are composed of one or more cells.
All cells arise from pre-existing cells.
Types of Cells
Prokaryotic Cells: Simple cells without membrane-bound organelles. Examples include bacteria.
Eukaryotic Cells: More complex cells containing membrane-bound organelles. Examples include plant and animal cells.
The Importance of DNA
DNA serves as the genetic blueprint for all living organisms. It carries instructions for development, functioning, growth, and reproduction.
Unit 2 đ˘
Cells
Cells: the basic unit of life
Prokaryotic Cells: no membrane bound organelles
Has ribosomes
Small in comparison to eukaryotic cells
Eukaryotic Cells: Membrane bound organelles
Endosymbiosis Theory: hypothesized that some prokaryotes begin to live together in symbiotic relationships with the smaller prokaryotes living inside larger ones
Nucleus: This structure controls the activities of a cell by holding the DNA
Organelles
Nucleus: Controls the activities of a cell by holding the DNA
The DNA of eukaryotes is enclosed within a membrane called the nuclear membrane or envelope
Prokaryoic DNA floats in the cytoplasm and is sometimes referred to as nucleoid (nucleus-like)
Cytoplasm/cytosol: Fluid filled space contains the nucleus and other organells
Makes up most of the volume of the cell
Plasma âcellâ membrane : holds the cell together
The membrane is important for transporting substances into and out of the cell
Ribosomes: Synthesize (make) proteins according to mRNA instructions
Evidence for common ancestry
Non-membrane bound
Endomembrane System: Group of membrane bound organelles that work together to modify and package materials
Er, Golgi Complex, Lysosomes, Vacuolies, Vesticles, Nuclear Membrane
Endoplasmic reticulum: Plays a role in intracellular transport
Rough Er: helps sysnthesize and package proteins
Smooth ER: helps synthesize lipids and breakdown catbs
Helps detoxify the blood
Golgi Apparatus: Folds, modifies and synthesizes cellular products and packages proteins for trafficing
Makes glycoproteins
Mitochondria: Performs the process of cellular respiration
Double membrane allows for different compartments for different metabolic reactions
Has its own DNA
Evidence for endosymbiotic theory
Mitocondria has its own DNA and does itâs own reacions; cell respirations.
Lysomsomes: help carry out the process of cellular digestion
Contains hydrolytic enzymes
Plays a role in apoptosis
Cell death when there isnât enough energy to live
Membrane bound
Vacuoles: plays different roles in animal and plant cells
Membrane bound
Plants: large vacuole maintains turgor pressure through water/nutrients storage
More tugor presser allows plant cells to maintain shape and hold water
Animals: more, smaller vacuoles that store cellular material
Chloroplast: Where photosynthesis takes plae
Has its own DNA, ribosomes, and enzymes
Has double membrane
Contains chlorophyll
Evidence of endosymbiotic theory
Cloroplast has itâs own DNA and use to be itâs own cells and prokaryote and
Size Matters: Cell size and efficiency
Cells that have large surface area to volume ratios are more efficient at exchanging materials with their environment
The smaller the ratio of the cell the more efficient
Organisms have certain adaptations that allow them to increase their surface area to increase their efficiency
Typically: smaller organisms= higher metabolic rate per unit body mass
Cellâs Bouncer: Plasma Membrane
Plasma membranes are made up of phospholipids
Phospolipids have hydrophilic heads and hydrophobic tails
Separates cells from their outside environment
Selectively Permeable: only allows certain materials in/out
Extracellular: outside the cell
Intracellular: Inside the cell
Proteins embedded into the membrane can be hydrophobic (Nonpolar sides groups) or hydrophilic (charged, polar side groups) or both
Hydrophilic regions are inside the interior of the protein or exposed to cytosol
Hydrophobic region of proteins make up protein surface
Peripheral Protein: on oen side of the membrane
Intergral Protein: embedded in the plasma membrane
Glycoprotein/glycolipidsL on the outside of the membrane for sgnalling
Cholesterol: lipid molecule functions to keep the membrane from being too fluid, and too permeable to soem small molecules.
helps to secure the proteins that are embedded in the membrane
helps to keep the cell membranes of plant cells from freezing solid in very cold temperatures
Let me in Please!: Membrane Permeability
Because the membrane is semi-permable, concentration gradents occur across the membrane
Small, Nonpolar molecules freely pass through the membran
N2, O2, CO2
Large polar molecules and ions have to move through the membrane with embedded channels and transport proteins
K+, Na+
The nonpolar hydrocarbon tails prevent these molecules from moving
Small, polar uncharged molecules pass through the membrane in small amonts
H2O, NH3
Let me in Please!: Membrane Transport
Passive Transport: movement of molecules from high concentration to low concentration without energy
Diffsion: molecules moving from high to low concentration through the membrane
Facilitated Diffusion: Requires transport or channel proteins
Aquapirins specifically transport water
Active Transport: requires the direct input of energy
In some cases, moves molecules from low concentration to high concentration
Endocytosis (Bulk Transport)L cell takes in large molecules by folding the membrane in on itself forming small vesticles
Requires energy
Exoocytosis (bulk transport): Internal vesicles release materials from cells by fusing with the membrane
Requires energy
Let me in Please!: Tonocity and Osmoregulation
Osmosis: type of diffusion. This means that water oves form area of high water concentration to areas of low water concentration. JUST WATER
Hypotonic enviroment: Lower concentration of solutes in the environment than a cell
Hypertonic Environment: Higher concentration of solutes than a cell in the environment
Isotonic Environment: The same concentration of solutes in the cell and in the environment
Water moves form hypotonic to hypertonic regions
High water potential to low water potetial
Water potential equation Ń° = Ń°p + Ń°s
Ń° = Water potential
Ń°p = pressure potential
Ń°s = solute potential
Ń°s - -iCRT
i = ionization content
C= molar concentration
R= pressure content (.0831)
T= Kelvin temperature
Flashcards
What is the basic unit of life?
Cells
What is the main difference between prokaryotic and eukaryotic cells?
Prokaryotes lack membrane-bound organelles. Eukaryotes have membrane-bound organelles.
Which organelle controls cell activities by holding DNA?
Nucleus
Where is DNA found in prokaryotes vs eukaryotes?
Prokaryotes: nucleoid region in cytoplasm. Eukaryotes: inside the nuclear envelope.
What is the function of ribosomes?
Synthesize proteins according to mRNA instructions
What is the endomembrane system?
Group of membrane-bound organelles that modify and package materials: ER, Golgi, lysosomes, vacuoles, vesicles, nuclear membrane.
Rough ER vs Smooth ER functions
Rough ER: synthesizes and packages proteins. Smooth ER: synthesizes lipids, breaks down carbs, detoxifies.
Function of the Golgi apparatus
Modifies, folds, and packages proteins. Makes glycoproteins.
Mitochondria key features
Double membrane, compartmentalization, own DNA. Evidence for endosymbiosis.
Function of lysosomes
Intracellular digestion with hydrolytic enzymes. Role in apoptosis.
Plant vs animal vacuoles
Plants: one large central vacuole for turgor. Animals: multiple smaller storage vacuoles.
Chloroplast traits and function
Site of photosynthesis. Double membrane, own DNA and ribosomes, chlorophyll. Endosymbiosis evidence.
Why are small cells more efficient?
Higher surface-area-to-volume ratio improves exchange.
Main components of the plasma membrane
Phospholipids, embedded proteins, cholesterol, glycoproteins, glycolipids.
Peripheral vs integral proteins
Peripheral: on one side of the membrane. Integral: embedded in the membrane.
Role of cholesterol in membranes
Prevents excessive fluidity and permeability. Stabilizes proteins. Helps prevent freezing in plants.
Molecules that freely cross bilayer
Small nonpolar molecules: N2, O2, CO2
Molecules requiring transport proteins
Ions and large polar molecules, e.g., K+, Na+
Passive transport definition
Movement from high to low concentration without energy.
Simple vs facilitated diffusion
Simple: directly through membrane. Facilitated: via channels or carriers.
Aquaporins
Channel proteins that transport water.
Active transport
Often moves molecules from low to high concentration using energy.
Endocytosis vs exocytosis
Endocytosis: intake via vesicles. Exocytosis: release via vesicle fusion.
Osmosis
Diffusion of water from high to low water concentration.
Hypotonic vs hypertonic vs isotonic
Hypotonic: lower solute outside. Hypertonic: higher solute outside. Isotonic: equal solute.
Direction of water movement
From hypotonic to hypertonic regions.
Water potential equation
Ψ = Ψp + Ψs, where Ψp is pressure potential and Ψs is solute potential (Ψs = âiCRT).
Unit 3đ˘
First law of Thermodynamics: Cells need to take energy from somewhere
Second law of Thermodynamics : Energy transfer leads to less organization
The Universe tends towards disorder (entropy)
Less energy to clean room, more mess in room
Energy input must exceed energy loss to maintain order.
Put more energy in that you are losing
Celllar processes that release energy can be coupled with cellular processes that require an input of energy
Using more energy than we have means we have to use a reaction that makes energy
Couples - Happens together
Exergonic
Will happen on itâs own. Makes energy
Endergonic
Need energy and needs to be paired with an exergonic reaction to maintain energy
Enzymes
Enzyme: Biological catalysts
Protiens that speed up the rate of chemical reactions by lowering the activation energy
Primary, Secondary, and Treterairy structures
Made with amino acids
All it does is lower the activation energy
Enzyme Specificity: Each enzyme catalyzes only one kind of reaction
Only one enzyme can fit into one group
â â â
Co-factors: Molecules that help enzymes in catalyzing a reaction
Inorganic co-factors are usually metal ions (Fe2+, Mg2+)
Vitamins are examples of organic co enzymes
Environmental Impact on Enzymes
If enzymes are outside of their optimal conditions, they will denature (Change shape)
Temperature and pH will have an effect
The concentration of substrates and products can also effect the rate of an enzyme-catazlysed reaction
An increase in substrate concentration will start off initially speeding up the reaction. Then, once all of the enzyme in solution is bound by substrate, the reaction can no longer speed up.
Saturation Point: This concentration of substrates where all of the enzyme in a reaction is bound by substrate
At this point, the reaction rate reaches a maximum velocity (V_max), and further increases in substrate concentration will not affect the rate of the reaction.
Reactions
Photosynthesis
Light dependent Reactions
Occurs in the chloroplast thylakoid membrane
Starting materials
Water: provides electrons for the ETC
Photons (light): Energy
Products
ATP
NADH
Light Dependent Reatcion
Photons (light) is absorbed by the chlorophyll in PS2
The energy from the excited photons in PS2 split H2O molecules into H+ and O2
Electrons from the split we loose electrons and used in the ETC
Excited electrons moved from PH2
Excited electrons - Move from low to hight
When the electrons move, H= is moved form the stroma to the thylakoid lumen, creating the proton/electrochemical gradient
Electrons reach PS1
PS! absorbs more hotons and excites the electrons
Excited electrons are used to fix NAD+ into NADPH in the stroma
NADPH is then used in the Calvin cycle )light independent reactions)
H+ gradient (high in lumen, low in stroma) drives ATP synthase
Converts ADP+P into ATP
Light Independent Reaction
Occurs in the stroma
Starting Materials
3CO2
9 ATP
6 NADPH
Products
G3P â Glucose
More
   1.Carbon Fixation: CO2 from the atmoshere is attached to the RUBP (5 carbon acceptor) by rubisco (enzyme)
Unstable 6 carbon intermediate is formed that immediately splits into 2, 3carbon molecules (PGA)
Reduction: the PGAs are reduced by AT and NADPH which makes G3p
ADP and NADP+ are sent back to the light reaction
Carbohydrate Output: for every 1 G3P, the cycle must fix 3 CO2 molecules
The G3 is later combined into larger carbohydrate molecules (glucose)
TLDR - Photosynthesis
Know where each stage happens
light reactions = thylakoid membrane/ lumen (ATP/NADPH produced)
Calvin cycle = stroma (used ATP/NADPH to fix CO2
Be able to explain chemiosmosis (proton gradients â ATP synthase) and how electron carriers move electrons
Understand Rubiscoâs role (COâ fixation) and the three core Calvin phases (fixation, reduction, regeneration). Rubisco is often tested conceptually (limitations, oxygenase activity/photorespiration may be discussed in context).
Glycolysis
Occurs in cytoplasm/cytosol
Glucose â 2 pyruvate + 2 ATP + 2 NADH
Glucose in phosphorylated by ATP â Glucose - 6 - phosphate
The results is phosphorylated again by another ATP â Fructose 1,6-biphosphate
6 carbon molecules is cleaved into 2, 3-carbon molecules
2 G3P
G3P is oxidized: NAD+ âNADH
Substrate level phosphorylation
4 ATP
Link Reaction/Pyrucate Oxidation
Happends in the mitochondrial matrix
Carbon removed: CO2 released
NAD+ â NADH
Remainign 2 carbon is attached to coenzyme A â Acetyl CoA (enters Krebsâs cycle)
Per glucose: 2 Pyruvate â 2 Acetyl CoA, 2 NADH, 2 CO2
Krebâs Cycle/Citric Acid Cycle
happens in the mitochondrial matrix
For 1 glucose there has to be two cycles, er 2 cycles
6 NADH
2 FADH2
2 ATP
4 CO2
ETC and Chemiosmosis/Oxidative Phosphorylation
Happens in the mitochondrial membrane
Goal: Use energy from NADH/FADH2 to pump H+ and create proton gradient
NADH donates electrons to complex 1
Electrons move down the chain
Energy used to mover H+ into intermembrane space
FADH2 donates electrons to Comples 2 (no proton pumping)
Electrons move via ubiquinone (Q) and cytochrome complexes
O2 is the final electron acceptor, combining with electrons + H+ turns into H2O
W/O oxygen, the ETC stops
Proton gradient builds in intermembrane space (igh H+ outside, low inside)
H+ flows back into the matrix through ATP synthase (Chemiosmosis)
ATP synthase phosporylate AD to lost of ATP
Main idea: Electron flow creates a gradient; the gradient powers ATP synthase
Environmental Imact on Enzymes
Light Dependent Reactions
Protein channel is used to charge the electrons
Light Indendent Reaction
Glycolysis
happens twice
Link Reaction/ Pyrucate Oxidation
Krebs Cycle
ETC and Chemiosmosis
Unit 4 đ˘
How do cells communicate?: Cell Phones
Cell use chemical signal to âtalkâ to each other
Autocrine: Cell talking to itself
Paracrine: Short distance
growth factors
like a dog and clothing
Juxtacrine/Direct contact: To a cell directly
A back and forth conversation with a friend
Gap junctions (animals) plasmodesmata (plants)
Endocrine: Long distance, through bloodstream
A paper airplane to your friend on the other side of the classroom
Hormones (from the back of your head to the location)
Big girl AP common questions
Quorum Sensing: Bacteria regulates population-based behaviors like biofilm formation
Smalls signals increase with the increasing population density. When the max is hit a gene expression is triggered.
Based on weight sensing
Epinephrine Signaling (adrenaline): when cells convert glycogen into usable sugar/energy
Flight or flight reaction
liver cells break down glycogen into glucose
smooth muscle cells in blood vessels tighten or loosen based on the type of receptor
Signal Transduction Pathways:
Stimulusâ Signal sent â Reception by target cell â transduction â cellular response
Stimulus â Signal Sent
Ligands: signals (molecule)
binding starts with a signal transduction
Very specific (think of enzymes): the correct cells get the signal;
Cells that donât have the right receptors wonât do a thing. This prevents unnecessary activation
Water soluble ligands are external while hydrophobic (fears water) ligans are intracellular (in and out of the cell)
Reception by Target cell
G-protein-coupled receptors (GPCRs): Active G-proteins, triggering a single pathway
Signal received, g-protein then activated an enzyme which starts the reaction.
Receptor tyrosine kinase (RTKs): Triggers multiple pathways; can lead to mutations like cancer
One signal can trigger many pathways at once. Harder to regulate leading to cancer.
Ligand-gated ion channels: Opens due to ligand binding and allows ions to pass.
Intracellular receptors: Used by steroid hormones, it directly affects gene expression
Transduction - After signal is recieved
Transduction: interactions between protein kinase and ATP which increase the signal received by ligand binding. â Signal is multiplied
Amplification happens when a single kinase activates many kinase in the next level of the cascade reaction â one kinase activates many kinases
Many ligands allows for places for control and regulation
Signals are always transduced (translated) into a different form until a new/another signal is sent to prevent the phosphorylation of ATP
Kinases stimulate pathways
Phosphatase shut off pathways â takes away the phosphate
Dephosporylation: Happens when phosphate enzymes remove the phosphates from the protein.
Secondary messengers: Small, non-polar, water-soluble molecules or ions that pass a signal; spread with diffusion
Cyclic-AMP: Responsible for activating the protein kinase cascade. Often works with adenylyl cyclase
Calcium ions: Common messenger and relays signals in G-protein and Tyosine Kinase Receptor pathways.
Cellular Response
Response: Cell respond when the cascade is reached
Gene Expression: gene information is used to make proteins through translation and transcription
Big girl AP questions
RTKs: Activates multiple pathways at the same time then amplifying the signal
Mutations when constant RTK activation leads to uncontrolled cell division. (cancer)
GPCR: happens when a ligands binds to a reception then causing confrontational change that activates a G-protein by exchanging GDP for GTP.
Like ADP to ATP
G-protein then activates enzymes or second messengers like cAMP
Steriod hormones: Pass thorough the plasma membrane and bind to intracellular receptors. The hormone-recptor complex acts as a transcript or factor, directly regulating gene expression.
Homie-ostasis: your normal
Homeostasis: maintained through feedback
Negative feedback: Maintains stability (want to stop the stimulus)
Regulating body temp, insulin response
Response stops stimuli
Positive feedback: Amplifies a response until it is complete (
Labor contractions, blood clotting
Big girl AP questions
Blood sugar regulation: WHen blood glucose is high, the pancreas released insulin, causing the cells to absorb glucose. When blood glucose is low, glucagon is released to break down glycogen into glucose
Labor Contractions: oxytocin is released, causing stronger contractions, stimulates more oxytocin and releases until childbirth occurs.
Thermoregulation (in mammals): When body temperature rises, sweating and vasodilation dissipate heat. When temperature drops, shivering and vasoconstriction conserve heat.
My toe, sis
Purpose of cell Division:
Unicellular: to reproduce
Multi-Cellular: growth, repair, replace dying/ dead cells
Parent and daughter cells are identical: DNA organelles, etc.
DNA in Cell Division:
Chromatin: Coiled DNA
Chromosomes: DNA that is wrapped tightly
Sister Chromatids: A chromosome that duplicated
Interphase: Cells are often in this phase the longest
NO division happens
3 phases of interphase: G1, S, G@
G0 phase: Optional part when cells exit the cell cycle and no longer divide
G1: Cells grow after the are âbornâ or created
S: DNA replicates prior to cell division
This happens before cell division so each daughter cell has a full set of DNA
G2: Cell finished growth: prepared to divide by making organelles, proteins, and membranes
G1 checkpoint: Checks for DNA damage before it replicates. Makes sure there is efficient space and nutrients for division
G2 Checkpoint: Makes sure DNA has been fully copied and there isnât damage to the DNA
M checkpoint: Makes sure there are proper chromosome alignment before division. Makes sure all chromosomes are attached properly to the spindles (little hairs that pull chromosomes apart)
Mitosis: cell division of somatic cells that makes identical daughter cells
Prophase: Chromosomes become visible, unclean envelope dissolves, centrosomes form and spinde fibers attach to the chhromsome
Metaphase: Chromosmes line up in the middle of the cell; centrosomes move to opposit side of the cell
Anaphase sister chromatids are lulled to opposite sides of the cell by the spindles
Telophase: centrosomes dissemble, nucli reform, chromosomes start to uncoil back into chromatin
Cytokinesis in animal cells: cleavage furrow. Where the breakage of the cells happen
Cytokinesis in plant cells: cell plate which become a cell wall that separates the resulting daughter cells
Role of cyclins
Cyclins: Proteins with concentrations that rise and fall throughout the cell cycle, acting as regulatory sununits that control CDK activity
CDKs: Enzymes that add phosphate grougs to other proteins, activating or deactivating them to control cell cycle events
How they work together
Activation: A specific cyclin pairs with a specific CDK
Phosphorylation: Activated compels the prophylaxes key target proteins
Progression: Phosphorylation triggers specific cellular events, pushing the cells into the next ohase
Cylcial Nature: Cyclins are degraded after their job is done. Inactivating the CDK and allowing the cycle to progress to the next stage, ensuring events happen in the correct order
Regulating Cell Cycle
Cancer: results from unregulated cell division due to mutations in proto-oncogenes or tumor suppressor genes
Examples:
p53 gene: Suppresses tumors; if mutated, cells evade apoptosis
Ras gene: Mutations can lead to constant cell division
Big girl AP questions
Tumor - suppressor gene Mutations: prevents apoptosis, allows damaged cells to accumulate mutations that contribute to tumor growth
Oncogenes: mutated proto-oncogenes that cause unregulated division
Common example is the RAs protein, when mutated, it remain constantly active, driving continuous cell divison
Chemotherapy: targets rapidly dividing cells by disrupting the spindles formation affecting the cancerous and (some) healthy cell
What is the Chi-Square
Big Idean: Data with variation. This helps to decide the differences between what is observed and what we expect are due to change or a real biological effect
Key question: Are the observed result significantly different from the expected results?
What is a Chi-square: Statically test that compares:
Observed values: What actually happened in the experiment
Expected values: What we predicted before collecting data
Important notes:
Larger value: greater difference between observed and expected
Smaller value: observed data closely matches expected data
Chi-square DOES NOT tell you why results differ, only whether they differ significantly
How to solve a Chi Squared Problem: LAST SLIDE
State the null hypothesis
No significant difference
Calculate
Unit 5 đ˘
Meiosis
prophase 1
Metaphase 1
Anaphase 1
Telophase & Cytokinesis
Prophase 2
Metaphase 2
Anaphase 2
Telophase & Cytokinesis
Takeaways
The separation of homologous chromosomes in meiosis 1 makes sure that each gamete gets a haploid (1n) of chromosomes
Each has both maternal and paternal chromosome
Causes of
Mendelian Genetics
Came up with modern genetics and really important laws while playing with pea plants. Work was accepted in the 20th century (1900s)
All genetic information is stored in DNA or RNA
All cells have the same sets of DNA, certain genes are activated or deactivated
Nuclear DNA and Mitochondrial DNA
Nuclear DNA comes from mom and dad, mitochondrial DNA comes from just mom
RNA is used to create proteins with ribosomes
All DNA has the same nucleotides (A,T,G,C)
Means we come from the same ancestor
Vocab
Allele: A version of gene that can be dominated or recessive
W/ mendelian genetics, all genes have two alleles (Aa)
Autosomal: On a chromosome that isnât on a sex chromosome
Diploid: A cells that has two complete sets of chromosomes. One from each parent (2n)
Haploid:
Phenotype: Physical appearance of an organism (PHenotype, PHysical)
Mom has brown eyes I have brown eyes
Genotype: the alleles that make up the trait (GEnotype, GEnes)
AA, Aa, aa
Dominant: Produces more proteins to overtake another trait
Aa - The big A takes over
Recessive: A trait that doesnât produce enough proteins or product that is overpowered by dominant traits
Can take over if it is aa
Homozygous Recessive: An organism that had two recessive alleles. The organism will have the recessive phenotype. The weak one is doubled
aa, bb, gg
Homozygous Dominant: An organism that has two dominant alleles. The dominate phenotype
AA, BB, GG
Heterozgous: An organism that has one dominant and one recessive allele. It will have the dominant phenotype
Aa, Bb, Gg
Applying Vocab: Punnet Square
Yellow Pea: YY
Green Pea: yy
50% for a green baby and 50% for a yellow baby
Laws of probability
Yellow and green baby (one of each)
P(A and B) - P(A) x P(B)
R- Cannot roll tonnge
r - Can roll tonnge
% for homo zygouous
% for heterozygoute
Punnett Square are called âmonohybridâ crosses
Mono - One
Hybrid - Mix
Cross - CrossâŚ
Dihybrid Crossess
Yellow vs Green
Round vs Wrinkled
9:3:3:1
9 will be RY ( Round and yellow)
3 will be Ry
3 will be rY
1 will by ry
Probability of green wrinkled
1/16
Probability of Yellow and round
9/16
Stuff isnât that Simple: Sex Linked
R: Not color blind
r: color blind
Probability of a son (XY) that is color blind
50%
Probability of a daughter (XX) that is color blind
100%
Making Predictions
Rules of probability can be used to predict the passage of single gene traits from parent to child
Can be helpful in determine if traits are Mendelian or not
We can predict the pattern of inheritance form analyzing trait and geneome date
Is this trait recessive? Dominant? Sex-linked? Linked genes?
Unit 6đ˘
Dna and RNA Structure
Genetic information is passed to the next generation thought the DNA (sometimes RNA) molecules
Prokaryotes - Circular DNA Eukaryotes - Linear DNA
They both can have plasmids: extrachromosomal circular molecules
DNa and RNA are nucleic acids
Nucleic Acids: Made up of nucleotides
Phosphate group + nitrogenous bases (letters) + 5 carbon sugar
Ribose in RNA and deoxyribose in DNA
T in DNA, U in RNA
Purines and Pyrimidines
Purines: 2 ringed nitrogenous bases
A and G
Pyrimidines: single ring nitrogenous bases
T (U) and C
DNA Replication
The replication process ensures the continuity of heredity information
happens in mitosis and meiosis (S phase)
New DNA is made from the 5â to 3â direction
DNA replication is semi-conservatives
Uses a DNA strand as a template for a new strand of complementary DNA
Replication happens in the nucleus for eukaryotes and in the cytoplasm for prokaryotes
Replication steps
Helicase - Unwinds the DNAâs double helix so replication origins are recognized and replication can start
Topoisomerase relieves tension as DNA unwinds
THis is called the replication fork (looks like a Y)
RNA primers - placed on DNA molecules by primase so DNA polymerase can start
w/o the primer DNA polymerase can't work or start
DNA polymerase - binds to the template strand and adds complementary nucleotides
Leading strand - grows continually form 5â to 3â direction toward the replication fork
Lagging strand - grows discontinuously away from the replication fork
SHort fragments made are called Okazaki Fragments
After lagging strand is made in fragments, DNA ligase closes the gaps between the fragments.
DNA replication Vocab
Helicases: enzymes unwind the DNA strands
Single Strand Binding Proteins: Bind to the unpaired DNA strands keeping them from repairing
Topoisomerase: help reduce the twisting and tangling while the DNA strand is being unwound
Primer: short stretch of RNA placed on the unwound parental DNA strands that acts as a template strand
Synthesized by primase
DNA Ligase: joins the sugar phosphate backbones of all the Okazaki fragments into a continuous DNA strand
DNA pol III: primary enzyme that works to synthesize the new strand
DNA pol I: removes primers and replaces them with the proper nucleotides
Nuclease: DNA cutting enzyme that cuts out the damaged parts of the strand and fills the space with nucleotides using the undamaged strand as a template
Telomerase: enzyme that helps keep the length of chromosomes; aids in replacing the DNA shortening that happens during duplication
Histones: responsible for DNA packing in chromatin
Transcription
Happens on ribosomes in the nucleus in eukaryotes and cytoplasm in prokaryotes
Sequence of bases and the structures of the molecule determines the RNa function
Messenger RNA (mRNA): carries information from DNA in the nucleus to the ribosome in the cytoplasm
Transfer RNA (tRNA)L binds to the specific amino acids and has anticodon sequences that base pair with codons on mRNA
tRNA is recruited to the ribosome during translation to generate the primary peptide sequence.
Ribosomal RNA (rRNA): functional building blocks of ribosomes
Transcription Steps
RNA polymerase: Binds to what is known as promoter DNA
DNA is a sequence that signals to start the genetic information for a particular gene
RNA polymerase unwinds and separates the DNA by creating a structure known as the transcription bubble. The bubble breaks the hydrogen bonds between nucleotides.
RNA polymerase adds RNA nucleotide to its âcopyâ by matching nucleotides to those on the antisense strand, missense strands, coding strand
Hydrogen bonds between RNA and DNA breaks, frees the new strand (mRNA) from helix
For cells w/o nuclei, RNA may undergo more steps before moving out of the nucleus. Steps may inclus splicing (editing of the sequence) , capping (attaching additional nucleotides to ends of the strand), or polyadenylation (addition of a tail of adenine bases).
The RNA (MRNA) strand is moved out of the nucleus via specialized pores in the nucleus.
RNA polymerase synthesizes new mRNA in the 5â-3â direction by reading the template DNA in the 3â-5â direction
Transcription: mRNA Procession
After mRNA is created:
A poly-A tail (A-A-A-A-A) is added to the end of the 3â strand of the pre-mRNA
Makes the mRNA more stable and last longer
A GTP cap is added on the end of the â end of the pre-mRNA
helps ribosome recongnize the mRNA
Introns are removed and exons are keeps by spliceosomes
Different versions of the genes can be made by removing/keeping different introns and exons
Called alternative splicing
Translation
Translation of mRNA happens on the ribosome that are located int he cytoplasm for both the prokaryotes and eukaryotes
Can happen on the ribosome on the rough ER on eukaryotes
In Prokaryote, transcription and translation happen at the same time
Translation Steps:
Initiation: rRNA in the ribosome interactions with the mRNA at the start codon (AUG)
Elongation: nucleotides on the mRNA is ready in triplets called codons
Each odcon encode for a specific amino acid
Different codons can code for the same amino acids
All living organisms use the same genetic code â shows evidence for common ancestry
tRNA brings in amino acids to the place specified by the codon on the mRNA
The amino acid being transferred to the growing polypeptide chain
Termination: elongation continues until the stop codon is reached (UAG, UAA, UGA) and a release factor releases all molecule from the process
Translation: A special Case
Retrovirus are a unique case in that they donât follow âcentral dogmaâ
Instead of DNA â mRNA â Protein, retroviruses form from RNA â DNA
The reverse transcription is done by the enzyme reverse transcriptase
Virus RNA goes into host organism, copies RNA genome into DNA
DNA integrates into the host organism then viral proteins are made but the host organism
Regulation of Gene Expression
Regulatory sequences: stretches of DNA that interacts with regulatory protein that control transcription
Some genes are inducible what other are constitutively expressed
Epigenetics: Changes that can affect gene expression with reversible modification of DNA or Histones
Histones: Proteins that DNA wraps around to package DNA into Nucleosomes
Operon: Segment of DNA that has a series of structural genes and control elements that regulates transcription of the genes
Promoter: Where RNA polymerase binds to begin transription
Operator: Where a repressor protein binds to prevent the initial binding of RNA polymerase to the promoter
Repressabe Operon: An operon that is on but can be turned off
Ex - Trp-operon, or the operton for the production of tryptophan
Operon is constantly âonâ, the represson protein is unable to bind to operator and the RNA polymerase is able to synthesize mRNA leading to the creation of proteins that make tryptophan
Extra tryptophan helps the binding of the operon repressor protein to the operator region
Inducible Operon: An operon that is off but can be turned on. Attached to the operator region and RNA polymerase canât bind to make mRNA
Ex: Lac Operon
Prevents lactose in environment, is converted to allolactose. This allolactose (in a sufficient amount), binds to the repressor protein, causing a change that doesnât allow the repressor to bind to the operator. Now the RNA polymerase can bind and produce enzymes that break down lactose for the cell.
Differentiation: Unspecialized stem cells become mature, specialized cells with distinct structures and functions. Drevign by selective gene expression ( when specific genes are being turned off and on)
Different activations of transcription factors âactivationâ different genes in different cells
Gene Expression and Cell Specialization
RNA polymerase and transcription factors bind to promoter or enhancer DNA sequences to start transcription
Sequences can be upstream or downstream of the target gene
Negative regulatory molecule inhibit gene expression by binding t DNA and blocking transcription
Results in differential gene expression and influences products and cell function
Organisms must be able to turn on and off certain genes in response to external stimuli for the environment. If not they might waste resources
DNA methylation addition of the methyl groups (CH3) to the DNA
Cause gege expression to stop
Histone acetylation: attachment of acetyl groups (COCH3)
Cause gene expression to increase and lossens the compactness of DNA
Methylation and acetylation can be inherited and reverse
Post transcriptional modifications can degrade protein and use amino acids later
Mutations
A mutation is an alteration in a DNA sequence that can cause changes in the type or amount of the protein produced and the consequent phenotype
Mutation are random or occur as a result of environmental causes.
If a severity is determined on the environmental context
mutations are the primary source of genetic information
Mutations can be beneficial, harmful, or neutral based on the effect or lack of effect on the resulting nucleic acid or protein and phenotypes that are produced from the change
Types of mutations
Point mutations: One nucleotide is substituted for a different ncleiotice
AKA - substitution
Frameshift Mutation: One or more nucleotides are inserted or deleted
Insertion or deletion mutation
Causes the codons to change
Nonsense Mutation: when a point mutation causes a premature stop
Silent Mutation: When the change in the nucleotide sequence has no effect on the amino acid sequence
Bacterial Changes
Transformation: Bacteria takes foreign genetic material(plasmids) from their environment then altering their genotype
Transduction: Viral transmission of genetic information
Conjugation: cell to cell transfer of genetic information
Transport: movement of DNA segments within and between DNA molecules.
Genetic Variation
All previously mention processes increase genetic variation
Reproductive processes that increase genetic variation are evolutionarily conversed and are shared by various organisms
Random assortment
Crossinf over
Random fertilization
Biotechnology
Biotech - Genetic engineering techniques can be used to analyze and manipulate DNA and RNA
Gel electrophoresis: process that seperates DNA fragments by size
Polymerase Chain Reaction: DNA fragments are amplified by denaturing (unzipping) DNA< annealing (sticking) rimers to the irginial strand, and extending the new molecule
DNA sequencing: Determins the order of the nucleotides in a DNA molecule
Results in DNA fingerprins that allows us to compare DNA sequences from different samples
Unit 7đ˘
Evolution: Change at the Population Level, not Individual
Evolution: Change in the genetic makeup/alleles frequencies in the populationâs gene pool
Individuals are born with a genotype and generally keep it for life, population evolve across generations
Genotype (the genes, what is inherited by the parents)
Alleles- AA, Aa, aa
An individual canât evolve because evolution requires changes in allele frequencies across generations
Individuals can acclimates (____): a short-term physiological (physical change) adjustment
Produce more red blood cells at high altitude
Develop: changing phenotype as the grow
The changes do non alter the DNA passed to offspring
Natural selection acts on individualsâ phenotype but evolution is measured as genetic change in the population
Natural Selection: Genetic Variation
Genetic Variability: The differences among individuals in a population
Natural Selection can only occur if some individuals already has some heritable variants (traits that can be passed down) that increase evolutionary fitness in that environment
More genetic variation a population has the more it will be the gene that will save the population when the conditions change.
Natural selection cannot make useful traits on demand, it sorts existing heritable variation. Variation must exist first.
Sources of Gentic Varation
Mutations: random changes in DNA sequences that create new alleles
Most mutations are bad or neutral but there will be an occasional benefit.
Recombination in Sexual reproduction: Prduces new combination of existing alleles
Crossing over in meiosis (prophase I)
Independent assortment of homologous chromosomes
Random fertilization
Many traits depend on both gene and environment: genes provide potential and the environmenat influences expression
Selection acts on phenotypes but only heritable (genetically influenced) phenotypic differences can cause evolutionary change.
Typical qustion
Show changes in an individual
Show what traits can respond to natural selection
Explain how mutations and recombination generate variation
DONâT SAY
Saying organisms âmutate because they need to.â Instead, mutations arise randomly; selection changes frequencies.
Treating acclimation as evolution.
Forgetting that selection acts on phenotype but evolution is measured genetically.
Darwinâs Logic, Machanisms, and Patterns
Darwinâs reasoning can be summarized as a set of observations and inferences - if true.. XYZ will happen:
Each species produces more offspring that can survive
Offsprink compete with one another for limited resources
Organisms in every population vary
Individuals with favorable heritable trait are more likely to be passed to subsequent generations
A reliable way to analyze selection scenarios is to check four conditions:
Variation: individuals different in a trait
Heritablility: Some of that variation is genetic and can be passed to offspring
Overproduction/competition: more offspring are produced that can survive; limited resources
Differential reproductive success:; individuals with certain traits leave more viable. .fertile offspring
Evolutionary Fitness: reproductive success (alive babies)
Amount of babies that can make more babies
Fitness is dependent on the environment and can change when biotic (living) and abiotic (non-living) factors
Different genetic variations can be selected for in different generations
Fitness in not just strength or longevity. A trait can reduce survival yet still be favored if it increases reproduction
Diffferential Selection: Favors one etream phenotype shifting the population mean
peppered moths changing color during industrial revolutionâs pollution
Increased beak depth during drought if harer seeds domuinate
Stabulizinf Selection: Favors intermediate phenotypes and reduces variation
Human birth weight (small and big babies didnât live long)
Disruptive Selection: Favors both extreams over intermediates, potentially increasing variation and sometimes contributing to specuation. It doesnât automatically produce speciation, it requires reduced gene flow and the evolution of reproductive isolation
Birds with small or large beaks get most food but the food is usually small or large
Types of Selection
Selectual Selection: types that improve mating success
Intrasexual selection*:* competition within one sex (often male-male competition)
Intersexual selection: mate choice (often female choice)
ADD EXAMPLES
Typical Questions patters:
Given data (survival rates), explains how natural selection changes allele frequencies
Interpret trait distribution graphs and identify
Distinguish survival advantage from reproductive advantage (fitness) and connect fitness to specific biotic/abiotic pressures.
Explain why acquired-traits idea does not produce population-level allele-frequency change.
Common Mistakes:
Distinguish survival advantage from reproductive advantage (fitness) and connect fitness to specific biotic/abiotic pressures.
Explain why acquired-traits idea does not produce population-level allele-frequency change.
Artifical Selection: Human Driven Change
Artificial Selection: occurs when human intentionally choose what they traits they want
It is evolution because allele frequencies change across generations, but the selecting agent is human preference rather than the natural environment
Artificial selection often reduces genetic diversity, especially when breeders use a narrow subset of individuals repeatedly.
Typical question patterns:
Compare natural selection and artificial selection (same logic, different selecting agent).
Predict consequences of selective breeding on genetic variation.
Identify whether a scenario is artificial selection or natural selection caused by humans.
Common mistakes:
Labeling antibiotic resistance as artificial selection.
Forgetting that selection requires heritable variation.
Assuming artificially selected traits always increase fitness in nature.
Population genetics: Measuring Evolution
Population Genetics: connects Mendelian genetics to evolution by tracking how allele frequencies change over time
Mendelâs law scale up to populations, allowing predictions about genotype frequencies when specific conditions are met
For a gene with two alleles, A and a:
Allele frequency is the fraction of all alleles in the gene pool that are A versus a.
Genotype frequency is the fraction of individuals that are AA, Aa, or aa
Because diploid individuals carry two alleles, allele frequencies are often calculated by counting alleles
The Hardy-Weinberg Model: describes an ideal population in which allele frequencies do not change from generation to generation
In AP Biology, HWE functions as a null hypothesis: if observed genotype frequencies match HWE expectations (given the assumptions), there is no evidence of evolution at that gene under those conditions.
If observed frequencies differ, one or more assumptions are violated.
For a two-allele system with allele frequencies p (A) and q (a):
p + q = 1
Expected genotype frequencies under HWE:
p2 + 2pq + q2 = 1
Where:
p2: the expected frequency of AA (homozygous dominant)
2pq:the expected frequency of Aa (heterozygous)
q2 the expected frequency of aa (homozygous recessive)
HWE requires:
Very large population size (minimizes random sampling effects).
Random mating with respect to the gene.
No natural selection among genotypes.
No migration (gene flow).
No mutation (or mutation negligible over the timeframe).
What happens if these conditions are not met:
If the population is small, it is more susceptible to random environmental impacts and sampling effects; allele frequencies can change by chance (genetic drift).
If mutations occur, new alleles are introduced and genetic equilibrium is disturbed.
If immigration or emigration occurs, individuals entering or leaving bring or remove alleles.
If mating is non-random, individuals choose partners based on certain traits; genotype frequencies shift (often more homozygosity), even if allele frequencies may not immediately change.
If natural selection occurs, organisms better adapted to the environment survive and reproduce more, so their alleles become more common.
Typical question patterns:
Given genotype counts, calculate allele frequencies and test HWE predictions.
Given recessive phenotype frequency, calculate p, q, and carrier frequency.
Interpret what a deviation from HWE suggests biologically and connect it to a violated assumption.
Common mistakes:
Confusing allele frequencies with genotype frequencies.
Using HWE equations without checking what the given value represents (allele vs genotype vs phenotype).
Claiming âthe population is evolvingâ without explaining which assumption is violated and how that changes allele frequencies.
Evolution: Mechanisms besides Natural Selection
Genetic drift (evolution by chance): random change in allele frequencies due to chance events, especially strong in small population
Drif can reduce genetic variation anc cancause alleles to become fixed or lost/. Drist isnât random, it is random sampling of which alleles gets passed on
Two important genetic drift events are:
Bottleneck effect: A bottleneck occurs when population size is drastically reduced (disaster, overhunting, habitat loss). The survivors may not represent the original gene pool, so allele frequencies can shift sharply.
Founder effect: occurs when a small group colonizes a new area. The new populationâs allele frequencies reflect the foundersâ alleles, not necessarily the source population.
In both cases, reduced variation can increase inbreeding and reduce a populationâs ability to adapt to future environmental changes.
Gene flow(migration): the transfer of alleles between population and reduce differences between populations
can increase genetic variation within a population and reduce differences between population
Gene flow is not automatically beneficial: migrants can introduce alleles poorly suited to the local environment, reducing local adaptation.
Mutation (source of new alleles): introduces new alleles into a gene pool. Mutation rates per gene are usually low, so mutation alone often changes allele frequencies slowly in the short term, but it is essential over long timescales because it replenishes variation.
Nonrandom Mating:Nonrandom mating (inbreeding, assortative mating) changes genotype frequencies by increasing homozygosity, even if allele frequencies do not necessarily change. This is a key reason random mating is a Hardy-Weinberg assumption.
Evidence for Evolution:
Fossil evidence, paleontology, and transitional features:
The fossil record documents that species have changed over time and that extinct organisms existed.
Although fossilization is rare and biased (hard parts fossilize more; some environments preserve better), the record reveals consistent sequences and transitional features.
Transitional features link groups by showing intermediate characteristics.
âTransitionalâ does not mean âhalf-evolvedâ or inferior; it indicates traits that help reconstruct evolutionary change across lineages.
Paleontology has also provided methods for dating fossils, including:
estimating the age of the rocks where a fossil is found,
measuring the rate of decay of isotopes (including carbon-14),
using geographical data.
Biogeography: the study of the distribution of flora (plants) and fauna (animals).
Patterns such as related species appearing in widely separated regions can be explained by common ancestry combined with migration, continental drift, and isolation.
Embryology: the study of development.
A classic comparative observation is that vertebrate embryos (fish, amphibians, reptiles, birds, mammals including humans) show fishlike features called gill slits (pharyngeal pouches). Similar developmental patterns are consistent with shared ancestry.
Comparative anatomy: Â Morphological homologies focus on anatomical structures shared across species.
Homologous structures: similar due to shared ancestry, even if they serve different functions (for example, forelimb bone patterns in mammals). Homology supports common ancestry.
Analogous structures: similar due to similar selective pressures, not shared ancestry (convergent evolution). A classic example is wings of birds and insects.
Vestigial structures: reduced remnants of features functional in ancestors. They support evolution because they make sense as historical leftovers rather than optimal design.
Molecular biology (DNA and protein comparisons)
Often the most compelling because all organisms use DNA/RNA and a largely universal genetic code. Mutations accumulate over time, and closely related species generally share more sequence similarity.
Common ancestry means that some original life-form is an ancestor of all life, with lineages branching over time.
Phylogenetic trees (often called cladograms in many classroom contexts) are used to study relationships among organisms and are built using fossil and/or molecular data.
Key interpretation rules:
A node represents a common ancestor.
Two taxa that share a more recent common ancestor are more closely related.
Rotating branches around a node does not change relationships; only the branching pattern matters.
Trees are not âladders of progress,â and taxa at the tips are not âmore evolvedâ than others.
Typical question patterns:
Distinguish homologous vs. analogous traits in scenarios.
Use molecular sequence comparisons to infer relatedness.
Interpret phylogenetic trees/cladograms to determine most recent common ancestors.
Identify which lines of evidence (fossils, biogeography, embryology, anatomy, molecular data) best support a claim.
Common mistakes:
Equating âsimilar functionâ with homology.
Reading phylogenies as a ranking of advancement.
Assuming the fossil record must be complete to be valid evidence.
Speciation: How new species form
Speciation: the process by which populations evolve into distinct species.
Biological Species Concept: species are groups of populations that can interbreed in nature and produce viable, fertile offspring, and are reproductively isolated from other such groups.
Speciation connects microevolution (allele-frequency change) to macroevolution (patterns above the species level) because accumulated genetic differences and reproductive barriers split lineages, increasing biodiversity.
Reproductive isolation: prevents gene flow between populations. Once gene flow is reduced or stopped, populations can diverge genetically through selection, drift, and mutation.
Prezygotic barriers (before fertilization): prevent fertilization.
Habitat isolation
Temporal isolation
Behavioral isolation
Mechanical isolation
Gametic isolation
Postzygotic barriers (after fertilization): relate to problems after fertilization, often involving hybrid survival or reproduction.
Reduced hybrid viability
Reduced hybrid fertility (a classic example is mules)
Hybrid breakdown
Allopatric Speciation: occurs when populations become separated by a geographic barrier (mountains, rivers, distance) so the two populations cannot interbreed. Gene flow drops, and divergence can occur via selection and drift until reproductive isolation evolves.
Sympatric speciation: occurs without a geographic barrier. Gene flow must be reduced through mechanisms such as strong selection, habitat differentiation, sexual selection, or chromosomal changes.
In plants, polyploidy (extra chromosome sets) can create near-instant reproductive isolation because polyploid individuals may not produce fertile offspring with the original diploid population.
Typical question patterns:
Identify prezygotic vs. postzygotic barriers in examples.
Predict whether speciation is more likely allopatric or sympatric given a scenario.
Explain how reduced gene flow leads to speciation and how reinforcement can strengthen barriers.
Interpret punctuated equilibrium vs. gradual change in terms of stasis and rapid divergence.
Common mistakes:
Treating speciation as individuals âdecidingâ not to mate (barriers evolve via genetic changes affecting traits like timing, behavior, or compatibility).
Treating speciation in animals as a single sudden mutation (usually gradual accumulation; polyploidy is the major âinstantâ case and mostly in plants).
Confusing âhybridâ with ânew speciesâ (hybrids can be sterile or unstable).
Forgetting that gene flow counters divergence.
Continued Evolution:
Antibiotic resistance: In a bacterial population, some cells may already carry alleles that provide resistance (often arising from prior mutation). When antibiotics are applied, susceptible bacteria die or reproduce less, resistant bacteria survive and reproduce, and resistance alleles increase in frequency. The antibiotic does not âteachâ bacteria to resist; it changes which bacteria leave descendants.
Misuse (overuse or incomplete courses) accelerates resistance by repeatedly applying selective pressure while leaving survivors to repopulate.
Pesticide and herbicide resistance: The same selection logic applies to agricultural pests and weeds. Resistance can evolve quickly when population sizes are huge, generation times are short, and selection pressure is intense.
Strategies such as rotating chemicals or maintaining refuges (areas without the pesticide) can slow resistance by keeping susceptible alleles in the gene pool, reducing the speed at which resistance fixes.
Evolution in response to climate change: As climates shift, selection pressures change. Populations may respond by evolving new trait distributions (if sufficient genetic variation exists), shifting geographic ranges (a non-evolutionary response that changes where populations persist), or declining if they cannot adapt fast enough.
Rapid environmental change can also reduce population size, increasing drift and reducing variation, which makes adaptation harder.
Conservation genetics: Genetic diversity functions like a toolkit: more diversity increases the chance that some individuals carry alleles helpful under new stresses (disease outbreaks, temperature changes).
Small, isolated populations face increased inbreeding (more homozygosity and expression of deleterious recessives), stronger drift (loss of alleles by chance), and reduced adaptive potential.
Conservation plans often aim to maintain habitat connectivity to support gene flow, while also considering risks such as outbreeding depression in some contexts.
Typical question patterns:
Explain antibiotic/pesticide resistance using natural selection steps.
Use before-and-after data to infer which genotype has the highest fitness.
Apply evolutionary reasoning to conservation scenarios (small populations, gene flow, inbreeding, drift).
Common mistakes:
Claiming individuals âbecome resistantâ during their lifetime.
Ignoring that resistance alleles must exist (via mutation/standing variation) before selection can increase them.
Confusing population decline (ecology) with allele-frequency change (evolution), though they can interact.
Orgins of Life on Earth
Oparin-Haldane hypothesis (early atmosphere chemistry): Alexander Oparin and J. B. S. Haldane proposed that the primitive atmosphere contained mostly inorganic molecules and was rich in methane (CH4), ammonia (NH3), hydrogen (H2), and water (H2O), with almost no free oxygen (O2).
This reducing atmosphere was proposed to facilitate the formation of organic molecules.
Miller-Urey experiment: Stanley Miller and Harold Urey simulated conditions thought to resemble primitive Earth by placing the proposed atmospheric gases into a flask and using electrical charges to mimic lightning. Organic compounds similar to amino acids appeared, supporting the idea that simple organic building blocks can form under plausible early-Earth conditions.
RNA-world hypothesis:
A common hypothesis is that the earliest life-forms were simple molecules of RNA. The RNA-world hypothesis suggests RNA could have served both as genetic material and as a catalyst (ribozymes), potentially preceding DNA and protein-based life.
Typical question patterns:
Describe what the Miller-Urey experiment tested and what its results imply.
Identify the gases proposed in the Oparin-Haldane model and the significance of low O2.
Explain the logic of the RNA-world hypothesis (why RNA is plausible as an early biomolecule).
Common mistakes:
Treating Miller-Urey as âprovingâ exactly how life began (it supports plausibility of abiotic synthesis under certain conditions).
Assuming early Earth had abundant O2 (the model emphasizes little free oxygen).